Abstract The cerebral cortex is the mammalian brain center for remarkable cognitive, perceptive, and motor capabilities, the execution of which depends on precise establishment of neuronal connectivity during development. Miswiring of cortical circuitry can contribute to developmental brain disorders. The formation of cortical circuits depends on both cell and non-cell autonomous mechanisms that underlie axon growth and pathfinding. These mechanisms are under precise transcriptional regulation that enables timely, coordinated expression of guidance cues and receptors to spatiotemporally control circuit wiring. Emerging studies have highlighted the roles of chromatin in transcriptional control, and defects in chromatin remodeling complexes are linked genetic disorders of brain developmental. The mechanisms by which altered chromatin regulation contributes to normal and disordered circuit development, however, remain incompletely understood. Coffin-Siris syndrome is a multi-system developmental disorder characterized by intellectual disability and agenesis of the corpus callosum. Genetic studies have shown that it is caused by loss-of-function mutations in subunits of the BAF (SWI/SNF-A) chromatin remodeling complex, a multi-subunit nucleosome remodeling complex that repositions nucleosomes along DNA, therefore contributing to transcriptional regulation of nearby genes. The BAF complex is well-studied in cancer and neural crest development. Its role in the developing cerebral cortex, however, is undefined. To gain insights into the function of the BAF complex in cortical development and circuit wiring, I conditionally deleted Arid1a, which encodes a key component of the BAF complex, from the developing cortex using Emx1-Cre or Nex-Cre. The current proposal is supported by my preliminary studies that the BAF complex plays an important role in cortical neural progenitor cells, but not post-mitotic neurons, for proper development of axon tracts that target the cortex. Importantly, I uncovered a potential non-cell autonomous role of this complex in the pathfinding of thalamocortical axons. Here I will test the central hypothesis that the BAF complex non-cell autonomously guides axon projections targeting the cortex by simultaneously regulating the expression of multiple guidance cues in neural progenitor cells. This work will: 1) define the cell and non-cell autonomous functions of the BAF complex in axon pathfinding; and 2) unbiasedly assess transcriptional alterations in the expression of axon guidance cues in the mutants, using mouse genetics, functional genomics and transcriptomics, and circuit neurobiology approaches. This work is perfectly in line with my long-term goal to understand the molecular mechanisms underlying the development and dysfunction of neural circuits in the cerebral cortex. This project will provide me with essential training in: 1) mouse genetics; 2) functional genomics and transcriptomics; and 3) in vivo gene manipulation propelling me towards my career goal of establishing an independent academic laboratory focused on characterizing the molecular mechanisms that underpin development and dysfunction of the cortical circuits.